Hydrothermal microwave method was used as a new route to synthesize pure BaTiO3 (BT) nanoparticles at 140°C for 10 min under rapid reacting with stoichiometric Ba/Ti ratio. The crystalline products were characterized by X-ray powder diffraction (XRD) and the structure was refined by the Rietveld method from the tetragonal structure, which was supported by the Ti K-edge X-ray absorption near-edge structure (XANES). The pre-edge of Ti in the XANES spectra indicated that titanium ions are localized in a nonregular octahedron. Typical FT-Raman spectra for tetragonal BaTiO3 nanoparticles presented well-defined peaks, indicating a substantial short-range order in the system. However, a scattering peak at 810 cm−1 was attributed to the presence of lattice OH− groups, commonly found in materials obtained by hydrothermal process. Besides, the peak at 716 cm−1 can be related to eventual Ba2+ defects in the BaTiO3 lattice. BaTiO3 (BT) nanoparticles presented spherical morphology with a non-uniform distribution of particle sizes. An intense and broad photoluminescence band was observed around the green color emission at room temperature. By means of an excitation energy of 2.54 eV (488 nm), it was noted that the maximum profile emission (2.2 eV) is smaller than the forbidden band gap energy of BaTiO3, indicating that certain localized levels within the band gap must exist.
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This paper reports an experimental and theoretical investigation of the effects of adding Fe to the perovskite strontium titanate SrTiO 3 . The effects include changes in the short-order range structure as well as in the electronic and electrical properties. X-ray diffraction analysis reveals that the
Registro de acceso restringido Este recurso no está disponible en acceso abierto por política de la editorial. No obstante, se puede acceder al texto completo desde la Universitat Jaume I o si el usuario cuenta con suscripción. Registre d'accés restringit Aquest recurs no està disponible en accés obert per política de l'editorial. No obstant això, es pot accedir al text complet des de la Universitat Jaume I o si l'usuari compta amb subscripció. Restricted access item This item isn't open access because of publisher's policy. The full--text version is only available from Jaume I University or if the user has a running suscription to the publisher's contents.
Ceria (CeO 2 ) plays a vital role in emerging technologies for environmental and energy-related applications. The catalytic efficiency of ceria nanoparticles depends on its morphology. In this study, CeO 2 nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The samples were characterized by X-ray diffraction, transmission electron microscopy, Raman scattering spectroscopy, electron paramagnetic resonance spectroscopy and by the Brunauer-Emmett-Teller method. The X-ray diffraction and Raman scattering results indicated that all the synthesized samples had a pure cubic CeO 2 structure. Rietveld analysis and Raman scattering also revealed the presence of structural defects due to an associated reduction in the valence of the Ce 4+ ions to Ce 3+ ions caused by an increasing molar fraction of oxygen vacancies. The morphology of the samples was controlled by varying the synthesis temperature. The TEM images show that samples synthesized at 80 C consisted of spherical particles of about 5 nm, while those synthesized at 120 C presented a mix of spherical and rod-like nanoparticles and the sample synthesized at 160 C consisted of nanorods with 10 nm average diameter and 70 nm length. The microwave-assisted method proved to be highly efficient for the synthesis of CeO 2 nanoparticles with different morphologies.
Micro-sized decaoctahedron BaZrO3 powders were synthesized by means of a hydrothermal microwave method at 140 °C for 40 min. The X-ray diffraction, Raman, UV−visible, and inductively coupled plasma atomic emission (ICP-AES) spectroscopy, as well as measurements of photoluminescence (PL) emission, were used for monitoring the formation of a perovskite phase with random polycrystalline distortion in the structure. Two emissions at 477 and 526 nm were accompanied by increase in the gap values, indicating the existence of different emission mechanisms. A theoretical model derived from previous first principle calculations allow us to discuss the origin of the photoluminescence emission in BaZrO3 powders which can be related to the local disorder in the network of both ZrO6 octahedral and dodecahedral (BaO12) hence forming the constituent polyhedron of BaZrO3 system. Initial observations of a novel morphology of the BaZrO3 perovskite crystal growth based on decaoctahedron shape is demonstrated and indirectly related to photoluminescence emissions.
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